Ammonia or urea may be stored on-board a vehicle for use as a reductant in exhaust emission control systems.
Under some conditions, such as during engine starting, ammonia vapor that was generated in the reductant system may be used, such as described in U.S. 2006/0117741. For example, ammonia vapors may be routed to a storage unit and a reactor that uses exhaust heat or electrically generated heat. Further, the vapors may also be directed to the exhaust gas to react with exhaust gas NOx in a catalyst in the exhaust flow, while reductant stored in a separate tank may also be delivered to the exhaust.
However, the inventors herein have recognized several issues with such a system. For example, a lack of coordination between vapor reductant and reductant delivered from the tank may result in insufficient reductant supply, or an over-supply of reductant. Further, uncertainties in the amount of vapors delivered may further exacerbate such issues, especially when vapor delivery is first commenced.
Thus, in one approach, a method of operating a reductant delivery and storage system of a vehicle may be used. This method comprises storing an ammonia-containing fluid in a first storage device, generating ammonia vapors in the first storage device and storing said generated ammonia vapors in a second storage device, purging said stored vapors from the second storage device to an exhaust of the engine, delivering said ammonia-containing fluid to said exhaust of the engine, and adjusting at least one of an amount of ammonia-containing fluid delivered and an amount of vapors purged to said exhaust based on the other of said at least one of said amount of ammonia-containing fluid delivered and said amount of vapors purged to said exhaust.
In this way, it may be possible to coordinate delivery of vapor reductant and a separate reductant supply from a storage tank, even under varying operating conditions. For example, during initial delivery of vapor reductant, the concentration of vapors may be identified and compensated via the delivery from the tank. Then, it may be possible to increase vapor delivery to effectively purge the storage of the vapors. In this way, effective coordination may be achieved. Further, as the vapor concentration varies during purging, adjustment in the reductant delivered from the tank may be used to maintain accurate control of total reductant delivery according to the engine operating conditions.